The present device provides automatic gain control of input signals, such as incoming RF signals, over a large dynamic range of input levels with a constant rise time.
The normal method for providing automatic gain control is to feed an AGC amplifier an input signal from the output of an IF amplifier and apply the AGC voltage back to the IF amplifier. The result is that input signal levels, which are greater than a small set value, saturate the AGC and IF amplifiers. Consequently the AGC amplifiers do not know the true value of the incoming input signal and cannot anticipate how much AGC to develop. All high levels of the incoming input signal appear approximately the same due to saturation. The result is that the AGC builds up differently for different input signal levels.